Can spider bots be attached to a spidertron? Instead of using the player's inventory and following the player, is there a way they can follow vehicles like a tank or a spidertron? I get that at that point you have normal bots, but it just seems very thematically cool to have spiderbots building stuff for the spidertron.

No, but also yes, sort of. They’ll use the player inventory, but if the player is in a spidertron they’ll prefer the spidertron inventory.
I do love the idea of spidertrons being able to deploy their own spiderbots though, that would be super cute and fun

Can you select a preference for which inventory is used? In some cases I'd rather the Spiderbots to use the players inventory when piloting a Spidertron rather than use from Spidertrons trunk?

Is it possible to take from both character and spidertrons inventory at the same time?

For now it is not possible to use both inventories simultaneously, but I will look into it for a future update.